1. Field of the Invention
The present invention generally relates to gateway apparatuses and packet routing methods, and more particularly, to a gateway apparatus and a packet routing method for establishing a dial-up connection between a local network comprising a plurality of terminals and an external network, and for routing packets between the local network and the external network.
Recently, the Internet is being used extensively. A user requiring a temporary connection to the Internet usually dials an access point of a provider offering Internet access so as to connect a user terminal to the Internet through the public network. Connection by dialing an access point is referred to as dial-up connection. The number of dial-up connection users is increasing.
FIG. 1 shows a dial-up connection method (packet routing method) according to the related art. Two main modes of dial-up connection are known. The first mode is referred to as dial-up connection of a terminal type (hereinafter, simply referred to as terminal connection). In terminal connection, a single terminal is connected to a desired network (for example, the Internet) through a modem or a terminal adaptor.
The second mode is referred to as dial-up connection of a network type (hereinafter, simply referred to as network connection). In network connection, a connecting end as well as the provider end forms a local network. This local network is connected to an external network on the OSI Network Interface Layer level, using a network routing device such as a dial-up router.
A modem, a terminal adaptor or a dial-up router is substantially equivalent to a gateway apparatus for connecting at least one terminal to an external network.
Usually, in terminal connection, a provider dynamically assigns a Layer 3 address to an accessing terminal. Therefore, the number of terminals connectable to the provider network per a unit time can be set to be greater than the total number of terminals that could potentially access the provider network simultaneously. Thus, the line can be utilized efficiently.
In terminal connection, a terminal is in one-to-one connection with a modem or a terminal adaptor, and if there is only one phone-circuit available, only one terminal can connect to an external network at a given time.
One advantage of terminal connection for a provider is that it is not necessary to manage local networks of users on the provider side and that a relatively large number of users can be accommodated easily. Accordingly, the access charge is relatively inexpensive.
In network connection, a plurality of terminals connected to a local network can communicate with an external network substantially simultaneously. Routing information for the individual terminals in the local network needs to be forwarded to the external network. The external network can distinguish the location of the terminals by the routing information, and can precisely transmit data to the corresponding terminal.
The above-described gateway apparatus and dial-up connection method according to the related art have the following disadvantages.
Terminal connection has a disadvantage in that, from the viewpoint of a user, only a single terminal can be connected to an external network.
Even if a plurality of terminals constitute a local network and the local network is connected to a dial-up connection interface having Network Interface Layer level routing functions, it is impossible for multiple communication sessions to take place simultaneously. In such a system, routing information is not supplied to the provider side. Accordingly, while packets can go out of such a system, no information is available as to where a reply packet from an access destination end system is to be delivered. Therefore, a reply packet can not be received properly by the corresponding terminal.
In order for routing information for individual terminals constituting a local network requesting a dial-up connection to be properly transferred, network connection is essential.
However, in network connection, the external network needs to maintain routing information for the individual terminals constituting the local network on the user side. Accordingly, a unique address unused by any other terminal in the global Internet needs to be assigned to each of the terminals requesting an access. Accordingly, in network connection, it is difficult to assign a Layer 3 address dynamically to the interface on the local network side.
In network connection, both the external network and the local network should be provided with facilities for ensuring that routing information is properly transmitted. Furthermore, advanced network management facilities such as security facilities should come into operation once the local network and the external network are mutually connected so that transparent application-level communication is initiated. Accordingly, due to the managerial complexity, the access charge for network connection is usually more expensive than that for terminal connection.